Electroweak Baryogenesis in Two Higgs Doublet Models and B meson anomalies

TL;DR

This study investigates electroweak baryogenesis within a minimal flavour-violating two-Higgs doublet model in light of the DO dimuon anomaly. It combines a one-loop finite-temperature potential, bubble-wall dynamics, and Boltzmann transport equations to calculate the baryon asymmetry, while enforcing a comprehensive set of phenomenological constraints. The findings indicate that a strong first-order phase transition and sufficient baryogenesis occupy a small, highly predictive region of parameter space, and that reconciling EWBG with the dimuon anomaly is challenging but not ruled out in some scenarios. The work also outlines clear collider signatures and EDM/B-physics constraints that will test these models in future LHC data and precision measurements.

Abstract

Motivated by 3.9 sigma evidence of a CP-violating phase beyond the standard model in the like-sign dimuon asymmetry reported by DO, we examine the potential for two Higgs doublet models (2HDMs) to achieve successful electroweak baryogenesis (EWBG) while explaining the dimuon anomaly. Our emphasis is on the minimal flavour violating 2HDM, but our numerical scans of model parameter space include type I and type II models as special cases. We incorporate relevant particle physics constraints, including electroweak precision data, b to s gamma, the neutron electric dipole moment, R_b, and perturbative coupling bounds to constrain the model. Surprisingly, we find that a large enough baryon asymmetry is only consistently achieved in a small subset of parameter space in 2HDMs, regardless of trying to simultaneously account for any B physics anomaly. There is some tension between simultaneous explanation of the dimuon anomaly and baryogenesis, but using a Markov chain Monte Carlo we find several models within 1 sigma of the central values. We point out shortcomings with previous studies that reached different conclusions. The restricted parameter space that allows for EWBG makes this scenario highly predictive for collider searches. We discuss the most promising signatures to pursue at the LHC for EWBG-compatible models.

Figures (13)

• Figure 1: One loop diagrams that induce an effective local operator of the charged scalar field $s^\pm$ to $\bar{u}_R \, d_L$ from a coupling to $\bar{u}_L \, d_R$. The largest contribution for the diagrams come from a top-bottom quark fermion loop in both cases.
• Figure 2: Potential at $T=T_c$ for a case that exhibits mild electroweak symmetry breaking in the quasi-symmetric minimum. The log of [V minus a constant near the minimum value] is plotted to exaggerate the barrier between the two minima.
• Figure 3: Left: distributions of parameters satisfying sphaleron and particle physics bounds, including ${\zeta}^{'0}_b$ and ${\zeta}^{'\pm}_b$, but not insisting on reproducing the magnitude of the observed $\rm DO \! \! \! \!/ \,$ dimuon excess. $m_{H,A}$ denote masses of the new scalar and pseudoscalar Higgs bosons, respectively. Normalizations are arbitrary. Masses are in GeV. Right: distributions from MCMCs in which ${\zeta}^{'0}_b = {\zeta}^{'\pm}_b \approx 0$, and either omitting (heavy black bars) or applying (narrow red bars) the constraints from EWPD, $b\to s \gamma$, neutron EDM, and perturbativity of couplings. Here $|\eta_U|,|\eta'_D|$ are proxies for $|{\zeta}^{0}_t|,|{\zeta}^{'0}_b|$.
• Figure 4: Scatter plot of baryon number in units of the observed density ($n_B/n_{B,\rm obs}$) versus the predictor $q$, Eqn. (\ref{['qeq']}).
• Figure 5: Left: the phase of $S^0$-field computed from the full EOM (solid black) and from the minimization of $V$ (red dashed) as a function of $zT$ corresponding to model 1 in table \ref{['tab:largeetaDmodels']}. Right: same for the $zT$ derivative of the phase.